8 bit color depth support

[kenc@attachmate.com]

Why is sub-15 bit color depth support disabled for the Windows platform (see WindowsGLDrawable.java) ?  I haven't tried X11 yet but it looks like it is not disabled there.  I didn't want to just make a feature request to add it because it was specifically disabled.  Someone must have had a good reason to do this.  I would like to be able to use overlay plane functionality in my video hardware but that is exclusively available in an 8 bit color depth  flavor only.

[Ken Russell]

We did this to avoid having to expose a notion of color palettes in the APIs. Setting and fetching color palettes in OpenGL is done with window system-specific APIs which would have meant introducing another abstraction for portability. Since it seemed that 8-bit graphics are on their way out anyway we decided to skip doing this. If you see a strong need even in the current world (what graphics card are you using?) then we can reconsider this for a future release.

[kenc@attachmate.com]

The issue with 8 bit support is getting at the overlay plane feature of high-end video cards that have it.  I have a mix of nVideo Quadro card and some ATI FireGL cards that have overlay hardware available through OpenGL.  I only have Windows installed on these systems.   The overlay planes are all associated with 8 bit color depth PFDs.  I'm pretty sure that these same cards can be used in Macs, under Linux and also Sun sells them with some of their x64 Solaris workstations.

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[Ken Russell]

My assumption, based on limited information, is that overlay planes never really took off as a concept and that it's possible to emulate their presence by changing how the app performs its rendering. Do you see a strong need for overlay planes in current or potential future applications?

[kenc@attachmate.com]

Overlay planes are a very powerful construct.  They are commonly used in 3D CAD and GIS.  For example  if you want to lay a 2D grid over the top of a 3D terrain map.  You would draw the grid in the overlay plane and the terrain map in the main plane.  You could draw/erase/change the grid without having to disturb the potentially (graphically) expensive terrain rendering.  Virtually all fancy-expensive-professional 3D video cards have user level exposed overlay planes.  Some even have multiple levels of overlay planes.

[GKW]

You can do the exact same thing with render to texture and have the added bonus that pretty much every videocard made in the last four years supports render-to-texture.

[kenc@attachmate.com]

But render to texture an nVidia specific OpenGL extension.  Certainly all nVidia cards have this that were made in the last 4 years.

[GKW]

Frame buffer objects can be bound as textures and are available on non-nvidia cards.

[kenc@attachmate.com]

It's still not the same.  Overlay planes are a completely separate pool of video memory (different drawing surface) from the main plane.  You can scribble all over them and not disturb the contents of the main plane.  It's a common hi-end feature available in the hardware and the native OpenGL that is not available through jogl.

[Ken Russell]

Do you really want to restrict your main rendering to 8 bits of color? Isn't that going to make it look badly posterized?

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[turquoise3232]

It's still not the same.  Overlay planes are a completely separate pool of video memory (different drawing surface) from the main plane.  You can scribble all over them and not disturb the contents of the main plane.  It's a common hi-end feature available in the hardware and the native OpenGL that is not available through jogl.

Hi, I have seen application using underlay / overlay functionality on Solaris system with very low price/quality cards but as GKW mentionned you can do the same with FBO and I am not sure that performance will be decrease with it... Did you give it a try?

[kenc@attachmate.com]

You don't use overlay planes for 'main rendering'.  You draw relatively simple stuff, like grid lines for a map that come and go or dynamically change, into the overlay planes and your fancy, expensive rendering goes to the high resolution, color rich main plane.

[Ken Russell]

OK, I misunderstood. I thought that you meant that overlay planes were only available for visuals with 8-bit color on your system.

Please feel free to file a bug with the JOGL Issue Tracker about this, but I can't guarantee that it will be addressed in as prompt a fashion as you would probably like. I would suggest you look into the alternatives that have been suggested here, although I realize that they aren't really the same thing as a true overlay plane.